In wireless communication networks, orthogonal frequency division multiplexing (OFDM) and multiple-input and multiple-output (MIMO) transceivers can improve reliability for frequency-selective fading channels over wider transmission bandwidths, and also exploit frequency-selective scheduling gains in multi-user cellular (mobile) networks.
Without requiring additional bandwidth, MIMO techniques provide an enormous increase in data rates needed to support ever expanding high performance wireless networks. Furthermore, MIMO techniques with OFDM modulation provide high data rate capabilities over wider transmission bandwidths with improved reliability against time-frequency-selective channel fading, multi-user diversity and interference mitigation in cellular networks.
To estimate the MIMO-OFDM wireless channel in spatial, temporal and frequency domains, it is a common practice in the prior art to explicitly transmit known pilot symbols along with the unknown transmitted data symbols, which need to be detected by the receiver.
However, separate transmission of the pilot symbols wastes power, time and bandwidth (frequency) that could otherwise be used to increase the data rate. More importantly, a fixed number of the pilot symbols might not be sufficient to estimate a rapidly varying channel. It is also inefficient to estimate a channel that does not vary appreciably with a fixed number of pilot symbols.
In existing networks designed according to the IEEE 802.11n, IEEE 802.16e and 3GPP LTE standards, for example, which are based on MIMO and OFDM technologies, known pilot symbols and unknown modulated data symbols span distinct and predetermined time-frequency resource units. That is, the pilot symbols and the data symbols do not overlap. Because many different configurations are possible in placing pilot symbols and data symbols in a time-frequency resource block (RB), in a non-overlapping fashion, the consequence is that design and implementation of conventional RBs are less flexible.
As examples, in conventional networks, the RB design for MIMO-OFDM networks with spatial-multiplexing (SMUX) is different from the RB design for MIMO-OFDM networks with space-frequency or space-time coding, such as Alamouti coding, see U.S. Pat. No. 6,185,258, Alamouti, et al., Feb. 6, 2001, “Transmitter diversity technique for wireless communications.”
In a similar manner, the conventional RB designs are extremely inflexible for some networks, such as multi-user MIMO-OFDM networks, MIMO-OFDM networks with multiple base-stations in cooperation (also referred to as coordinated multi-point transmission, CoMP), and cooperative communication networks that utilize multiple relay stations to increase reliability and enhance coverage.